高温下掺再生骨料及纤维混凝土物理力学性能研究

Experimental study on physical and mechanical properties of ultra-high performance concrete with recycled coarse aggregate and steel fiber under high temperature

目前关于可再生纤维混凝土的性能研究较为充分,但对其高温处理后性能变化认识不足。为此,针对超高性能混凝土(UHPC)、50%粗骨料替代超高性能混凝土(50%R-UHPC)以及50%粗骨料替代-1.0%钢纤维超高性能混凝土(50%R-1.0%S-UHPC)进行高温处理(200℃、400℃、600℃、800℃),研究高温对它们力学性能(单轴抗压强度、弹性模量、劈裂抗拉强度以及抗弯强度等)、抗渗性能以及导热性能的影响,并建立了各项性能指标与孔隙率之间的经验预测模型。研究结果表明:再生粗骨料的添加会弱化UHPC的力学性能、抗渗性能和导热性能,导致抗压强度、抗拉强度和抗弯强度降低,提高UHPC的孔隙率和渗透率;钢纤维的添加会提升UHPC力学性能和导热性能,但会弱化UHPC的抗渗性能。高温处理后UHPC的力学性能、抗渗性能和导热性能会逐渐减弱,并呈现出明显的温度门槛值效应,即400℃之前UHPC力学性能、抗渗性能和导热性能的弱化效应不明显,一旦超过温度门槛值后它们会迅速减弱;对于UHPC和50%R-UHPC来说,随着处理温度的升高,它们的力学性能和导热性能之间的差距会逐渐减小。

At present,the research on the performance of concrete with recycled coarse aggregate and fiber is relatively sufficient,but the understanding on its performance changes after high temperature treatment is insufficient.To this end,three types of concrete,namely ultra-high performance concrete(UHPC),50%recycled coarse aggregate UHPC(50%R-UHPC),and 50%recycled coarse aggregate-1.0%steel fiber UHPC(50R-1.0%S-UHPC),were treated under high temperature(200℃,400℃,600℃,800℃).Then the mechanical properties of the concretes,including uniaxial compressive strength,elastic modulus,splitting tensile strength,and flexural strength,as well as impermeability and thermal conductivity were studied.The results indicate that the addition of recycled coarse aggregate to the concrete weakens its mechanical properties,impermeability,and thermal conductivity,resulting in a decline in compressive,tensile,and flexural strength,as well as an increase in porosity and permeability.However,the addition of steel fibers enhances the mechanical properties and thermal conductivity of the concrete,but also results in an increase in porosity and permeability.High temperature treatment weakens the concrete mechanical properties,impermeability,and thermal conductivity,and there is a threshold temperature of 400℃.Prior to 400℃,the impact of high temperature treatment on these properties is minimal,but once the threshold is exceeded,the properties weaken rapidly.With respect to both UHPC and 50%R-UHPC,the differences in mechanical properties and thermal conductivity gradually diminish with the increase of the treatment temperature.